There are many ways they can get you...admit to two beers during the traffic stop, then fail their roadside sobriety tests. At that point, they have enough evidence to convict even without a BAC. Actaully the BAC might have saved you since it would be below the limit for most folks.

Of course few people can pass a field sobriety test...drunk or sober. All the cops I know have to practice those tests regularly so as to be able to perform them in court when asked to by the defense attorney.